Viscoelastic Polyurethane Foam with Aqueous Polymer Dispersion

ABSTRACT

A reaction system for forming a viscoelastic polyurethane foam includes an isocyanate component that has at least one isocyanate and an isocyanate-reactive component that is a mixture formed by adding at least a polyol component, an additive component, and a preformed aqueous polymer dispersion. The mixture includes, based on the total weight of the mixture, from 50.0 wt % to 99.8 wt % of a polyol component including at least one polyether polyol, from 0.1 wt % to 50.0 wt % of an additive component including at least one catalyst, and from 0.1 wt % to 6.0 wt % of a preformed aqueous polymer dispersion. The preformed aqueous polymer dispersion has a solids content from 10 wt % to 80 wt %, based on the total weight of the preformed aqueous polymer dispersion, and is one of an aqueous acid polymer dispersion or an aqueous acid modified polyolefin polymer dispersion in which the polyolefin is derived from at least one C 2  to C 20  alpha-olefin.

FIELD

Embodiments relate to viscoelastic polyurethane foams prepared using a preformed aqueous polymer dispersion and a method of manufacturing such viscoelastic polyurethane foams.

Introduction

Flexible, viscoelastic polyurethane foam (also known as slow-recovery foam and high-damping foam) is characterized by relatively slow, gradual recovery from compression and the viscoelastic foam may have a relatively lower resiliency. Exemplary applications for viscoelastic foam utilize the foam's characteristics such as shape conforming, energy attenuating, and/or sound damping. For example, the viscoelastic polyurethane foam may be used in comfort applications (such as bedding and pillows), shock absorbing applications (such as in athletic padding and helmets), and in soundproof applications (such as automotive interiors).

SUMMARY

Embodiments may be realized by providing a reaction system for forming a viscoelastic polyurethane foam that has a resiliency of less than or equal to 20% as measured according to ASTM D 3574, the reaction system including an isocyanate component that has at least one isocyanate and an isocyanate index of the reaction system is from 50 to 110; and an isocyanate-reactive component that is a mixture formed by adding at least a polyol component, an additive component, and a preformed aqueous polymer dispersion. The mixture includes from 50.0 wt % to 99.8 wt % of a polyol component, based on the total weight of the mixture, the polyol component including at least one polyether polyol, from 0.1 wt % to 50.0 wt % of an additive component, based on the total weight of the mixture, that includes at least one catalyst, and from 0.1 wt % to 6.0 wt % of a preformed aqueous polymer dispersion, based on the total weight of the mixture. The preformed aqueous polymer dispersion has a solids content from 10 wt % to 80 wt %, based on the total weight of the preformed aqueous polymer dispersion, and is one of an aqueous acid polymer dispersion or an aqueous acid modified polyolefin polymer dispersion in which the polyolefin is derived from at least one C₂ to C₂₀ alpha-olefin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary schematic representation of a melt-extrusion apparatus used to prepare a preformed aqueous polymer dispersion.

FIG. 2 illustrates the wetting effect of Working Example 12.

FIG. 3 illustrates the wetting effect of Comparative Example D.

DETAILED DESCRIPTION

A viscoelastic polyurethane foam may be characterized as having a resiliency that is less than or equal to 20% as measured according to ASTM D 3574 (may also be referred to as a Ball Rebound Test). For example, the resiliency may be less than 15%, less than 10%, less than 8%, and/or less than 7 wt %. The resiliency may be greater than 1%. Viscoelastic polyurethane foams may be prepared using a reaction system that includes an isocyanate component and an isocyanate-reactive component. In particular, the viscoelastic foam is formed as the reaction product of the isocyanate component and the isocyanate-reactive component. The isocyanate component includes at least one isocyanate such as an isocyanate-terminated prepolymer and/or a polyisocyanate. The isocyanate-reactive component includes at least one compound having an isocyanate reactive hydrogen atom group, such as a hydroxyl group and/or an amine group. The isocyanate component and/or the isocyanate-reactive component may include an additive such a catalyst, a curing agent, a surfactant, a blowing agent, a polyamine, and/or a filler.

According to embodiments, the isocyanate-reactive component includes at least three components. In particular, the isocyanate-reactive component includes a polyol component, an additive component, and a preformed aqueous polymer dispersion.

The polyol component accounts for 50.0 wt % to 99.8 wt % (e.g., 60.0 wt % to 99.8 wt %, 70.0 wt % to 99.5 wt %, 80.0 wt % to 99.0 wt %, 90.0 wt % to 99.0 wt %, etc., so as to be the majority component in the reaction system for forming the viscoelastic polyurethane foam) of the isocyanate-reactive component. The polyol component includes at least one polyether polyol and may optionally include at least one polyester polyol.

The additive component may include a catalyst, a curing agent, a surfactant, a blowing agent, a polyamine, water, and/or a filler. The additive component accounts for 0.1 wt % to 50.0 wt % (e.g., 0.1 wt % to 40.0 wt %, 0.1 wt % to 30.0 wt %, 0.1 wt % to 20.0 wt %, 0.1 wt % to 15.0 wt %, 0.1 wt % to 10.0 wt %, 0.1 wt % to 5.0 wt %, etc.) of the additive component, based on the total weight of the isocyanate-reactive component. The additive component in exemplary embodiments includes at least one catalyst and at least one surfactant.

The preformed aqueous polymer dispersion accounts for 0.1 wt % to 6.0 wt % (e.g., 0.1 wt % to 5.0 wt %, 0.1 wt % to 4.1 wt %, 0.1 wt % to 4.0 wt %, 0.1 wt % to 3.5 wt %, 0.1 wt % to 3.0 wt %, 0.4 wt % to 2.5 wt %, 0.5 wt % to 2.4 wt %, etc.) of the isocyanate-reactive component. The preformed aqueous polymer dispersion is one of an aqueous acid polymer dispersion or an aqueous acid-modified polyolefin polymer dispersion in which the polyolefin is derived from at least one C₂ to C₂₀ alpha-olefin (e.g., at least one C₂ to C₁₀ alpha-olefin and/or C₂ to C₈ alpha-olefin). The preformed aqueous polymer dispersion has a solids content from 10 wt % to 80 wt %, based on the total weight of the preformed aqueous polymer dispersion. The aqueous polymer dispersion may be a combination of one or more aqueous polymer dispersions that are used to form the viscoelastic polyurethane foam.

The viscoelastic foam prepared using the preformed aqueous polymer dispersion additive may have an air flow greater than 5.0 standard cubic foot per minute (scfm) (approximately 2.4 L/s) under standard conditions. The viscoelastic foam may have a recovery time (also referred to as viscoelastic recovery time) of less than 20 seconds (e.g., less than 10 seconds and/or less than 5 seconds). For example, a viscoelastic polyurethane foam may be prepared that has an increased air flow without sacrificing resiliency.

Preformed Aqueous Polymer Dispersion

The aqueous polymer dispersion includes at least (a) a base polymer including an acid polymer and/or an acid-modified polyolefin polymer and (b) a fluid medium (in this case water), in which the base polymer is dispersed in the fluid medium. The preformed aqueous polymer dispersion may be a continuous liquid phase component at ambient conditions of room temperature and atmospheric pressure and is derived from a liquid phase (i.e., the fluid medium) and a solid phase (i.e., the base polymer).

In embodiments, the preformed aqueous polymer dispersion is one of an aqueous acid polymer dispersion or an aqueous acid-modified polyolefin polymer dispersion in which the polyolefin is derived from at least one C₂ to C₂₀ alpha-olefin. By aqueous acid polymer dispersion it is meant an aqueous dispersion prepared with an acid based polymer. By aqueous acid-modified polyolefin polymer dispersion it is meant an aqueous dispersion prepared with an acid-modified polyolefin polymer. By derived from at least one C₂ to C₂₀ alpha-olefin it is meant that the polyolefin is a polymer prepared using at least one alpha-olefin, in which each alpha-olefin used is one of a C₂ to C₂₀ alpha-olefin (e.g., the polyolefin may be derived from at least one of ethylene, propylene, butylene, hexene, and/or octene). In exemplary embodiments, the polyolefin may be an ethylene based polymer and/or a propylene based polymer

As used herein, by polymer it meant a compound prepared by polymerizing monomers, whether of the same or a different type. Thus, the term polymer embraces the term homopolymer, usually employed to refer to polymers prepared from only one type of monomer, and the term interpolymer. It also embraces all forms of interpolymers, e.g., random, block, homogeneous, heterogeneous, etc. By copolymer/interpolymer it is meant a polymer prepared by the polymerization of at least two different types of monomers. These terms include both classical copolymers, i.e., polymers prepared from two different types of monomers, and polymers prepared from more than two different types of monomers, e.g., terpolymers, tetrapolymers, etc.

By ethylene based polymer it is meant a polymer that includes a majority weight percent polymerized ethylene monomer (based on the total weight of polymerizable monomers), and optionally may comprise at least one polymerized comonomer different from ethylene (such as at least one selected from a C₃ to C₂₀ alpha-olefin) so as to form an ethylene-based interpolymer. For example, when the ethylene-based polymer is an ethylene-propylene copolymer, the amount of ethylene may be greater than 50 wt %, based on the total weight to the copolymer. “Units derived from ethylene” and like terms mean the units of a polymer that formed from the polymerization ethylene monomers.

By propylene based polymer it is meant a polymer that includes a majority weight percent polymerized propylene monomer (based on the total weight of polymerizable monomers), and optionally may comprise at least one polymerized comonomer different from propylene (such as at least one selected from a C₂ and C₄ to C₂₀ alpha-olefin) so as to form an propylene-based interpolymer. For example, when the propylene-based polymer is a propylene-ethylene copolymer, the amount of propylene may be greater than 50 wt %, based on the total weight to the copolymer. “Units derived from propylene” and like terms mean the units of a polymer that formed from the polymerization propylene monomers.

Exemplary aqueous acid polymer dispersion may include ethylene-acrylic acid interpolymers, ethylene-methacrylic acid interpolymers, and/or ethylene-crotonic acid interpolymers. The ethylene-acrylic acid interpolymer is prepared by the copolymerization of at least ethylene and acrylic acid. The ethylene-methacrylic acid interpolymer is prepared by copolymerization of at least ethylene and methacrylic acid. The ethylene-crotonic acid interpolymer is prepared by copolymerization of at least ethylene and crotonic acid. It is understood that in such an aqueous acid polymer dispersion, exemplary embodiments are not limited to just ethylene-acrylic acid interpolymers, ethylene-methacrylic acid interpolymers, and/or ethylene-crotonic acid interpolymers. For example, ethylene can be copolymerized with more than one of the following: acrylic acid, methacrylic acid, and/or crotonic acid.

Exemplary aqueous acid polymer dispersions may include at least one ethylene-acrylic acid (EAA) copolymer (and/or ethylene-methacrylic acid copolymer) as the base polymer that is dispersed in the fluid medium (in this case water). The dispersion may be enabled by BLUEWAVE™ Technology, which is a proprietary and patented mechanical-dispersion technology that is a trademark of The Dow Chemical Company or an affiliated company of The Dow Chemical Company. For example, the EAA may be prepared by copolymerization of ethylene with acrylic acid, which yields ethylene-acrylic acid EAA copolymers. The ethylene-acrylic acid copolymer may have an acrylic acid content of at least 10 wt % (e.g., from 10 wt % to 70 wt %, from 10 wt % to 60 wt %, from 10 wt % to 50 wt %, from 10 wt % to 40 wt %, from 10 wt % to 30 wt %, and/or from 15 wt % to 25 wt %). Exemplary EAA copolymers are available as PRIMACOR™ products, available from THE DOW CHEMICAL COMPANY. The EAA copolymer may have a melt index from 100 to 2000 g/10 minute (ASTM Method D-1238 at 190° C. and 2.16 kg). The EAA copolymer may have a Brookfield viscosity from 5,000 to 13,000 cps at 350° F., and is available from The Dow Chemical Company.

The ethylene-methacrylic acid copolymer may be prepared by copolymerization of ethylene with methacrylic acid. Exemplary, ethylene-acrylic acid, ethylene-methacrylic acid, and/or ethylene-crotonic acid copolymers are discussed in U.S. Pat. Nos. 4,599,392 and/or 4,988,781.

Exemplary aqueous acid-modified polyolefin polymer dispersions include dispersions sold as HYPOD™ products, available from The Dow Chemical Company. The HYPOD™ products may be enabled by BLUEWAVE™ Technology, which is a proprietary and patented mechanical-dispersion technology that is a trademark of The Dow Chemical Company or an affiliated company of The Dow Chemical Company. BLUEWAVE™ Technology may utilize a high-shear mechanical process that may work by taking traditional thermoplastic polymers and elastomers and breaking them up into submicron particles. The aqueous acid-modified polymer dispersions may include propylene based dispersions and ethylene-based dispersions, which may combine the performance of high-molecular-weight thermoplastics and elastomers with the application advantages of a high-solids waterborne dispersion. The polyolefin of the dispersion may be a metallocene catalyzed polyolefin. Exemplary polyolefins are sold in the AFFINITY™, ENGAGE™, VERSIFY™, and INFUSE™ products, available from The Dow Chemical Company.

The aqueous polymer dispersion may be prepared by using a neutralizing agent. Exemplary neutralizing agents include ammonia, ammonium hydroxide, potassium hydroxide, sodium hydroxide, lithium hydroxide, and combinations thereof. For example, if a polar group of the base polymer is acidic or basic in nature, the polymer may be partially or fully neutralized with a neutralizing agent to form a corresponding salt. With the acid polymer modified dispersion prepared using EAA is used, the neutralizing agent is a base, such as ammonium hydroxide, potassium hydroxide, and/or sodium hydroxide. Those having ordinary skill in the art will appreciate that the selection of an appropriate neutralizing agent may depend on the specific composition formulated, and that such a choice is within the knowledge of those of ordinary skill in the art.

The aqueous polymer dispersion may be prepared in an extrusion process, e.g., as discussed in U.S. Pat. No. 8,318,257. FIG. 1 illustrates an exemplary a schematic diagram of an extrusion apparatus for manufacturing an aqueous polymer dispersions. An extruder 1 (such as a twin screw extruder) may be coupled to a pressure control device 2 (such as a pressure control valve, a back pressure regulator, a melt pump, and/or a gear pump). A neutralizing agent reservoir 3 and an initial water reservoir 4, each of which includes a pump (not shown), may be provided in connection with the extruder 1. The desired amounts of neutralizing agent and initial water are provided from the neutralizing agent reservoir 3 and the initial water reservoir 4, respectively. Any suitable pump may be used, e.g., based on the desired flow. The neutralizing agent and initial water may be preheated in a preheater.

Polymer resin (such as an acid polymer and/or a polyolefin polymer) may be fed from the feeder 7 to an inlet 8 of the extruder 1, where the resin is melted or compounded. The polymer resin may be provided in the form of pellets, powder, and/or flakes, for example. A dispersing agent may be added to the extruder through and along with the polymer resin or may be provided separately to the extruder 1. For example, the polymer (and dispersing agent if included) may be melted, mixed, and conveyed by screws in a mix and convey zone. The polymer resin melt is then delivered from the mix and convey zone to an emulsification zone of the extruder where the initial amounts of water and neutralizing agent (from the reservoirs 3 and 4) are added through an inlet 5. The resultant emulsified mixture may be further diluted at least one time using an additional water via inlet 9 from reservoir 6 in a dilution and cooling zone of the extruder 1. As would be understood by a person of ordinary skill in the art, at least in view of U.S. Pat. No. 8,318,257, the dilution scheme of the resultant emulsified mixture may be varied (e.g., based on the desired solids content). For example, the emulsified mixture may be further diluted with additional dispersion medium from additional reservoirs in a dilution zone of the extruder 1. The dispersion may be diluted to at least 30 weight percent dispersion in the dilution zone.

With respect to the screws in the mix and convey zone, one or more rotating restriction orifices may be located along the screw. The rotating restriction orifice may improve stability of the dispersion forming process. Non-rotating restriction orifices may be used. The screws may include high-mixing kneading disks, in some embodiments. In addition to the high-mixing kneading disks 60 described above and optionally low free volume kneading disks 62, which may minimize the volume weighted particle size distribution of dispersions formed using the extruder 1.

The extruder 1 includes high internal phase emulsion creation (HIPE) zones along a length thereof, e.g., as discussed in U.S. Pat. No. 8,318,257. For example, the aqueous polymer dispersion may be prepared using a system that incorporates 12 HIPE zones, in which the temperature is varied in the zones. Depending upon the feed composition (such as the polymer, dispersing agent, neutralizing agent, etc.), it may be desirable to have a longer or a shorter HIPE zones. Multiple dispersion medium injection points may be provided to allow the HIPE zones to be extended or shortened as needed. As the particle size of the dispersed polymer particles is formed in the HIPE zone, adequate mixing should be provided to develop the desired particle size. Having a variable length for the HIPE zone may allow for a broader range of polymers to be processed in a single extruder, providing for process flexibility, among other benefits.

The twin screw extruder barrels, screws, and dilution medium injection points may be varied such that the length to diameter (L/D) of the HIPE zone is at least 16 when producing EEA containing dispersions. The apparatuses described above may be used to produce dispersions, where, in some embodiments, the polymer feed rate may range from about 50 to about 2000 lb/h (about 22 to about 907 kg/h). In other embodiments, the polymer feed rate may range from about 100 to about 1000 lb/h (between about 45 and about 454 kg/h). In other embodiments, the screw speed may range from about 300 rpm to about 1200 rpm. In yet other embodiments, the extruder discharge pressure may be maintained at a pressure ranging from about 300 to about 800 psig (from about 21 bar to about 56 bar).

Polyol Component

The polyol component includes at least one polyether polyol and/or polyester polyol. Exemplary polyether polyols are the reaction product of alkylene oxides (such as at least one ethylene oxide, propylene oxide, and/or butylene oxide) with initiators containing from 2 to 8 active hydrogen atoms per molecule. Exemplary initiators include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butane diol, glycerol, trimethylolpropane, triethanolamine, pentaerythritol, sorbitol, ethylene diamine, toluene diamine, diaminodiphenylmethane, polymethylene polyphenylene polyamines, ethanolamine, diethanolamine, and mixtures of such initiators. Exemplary polyols include VORANOL™ products, available from The Dow Chemical Company. The polyol component may include polyols that are useable to form viscoelastic polyurethane foams.

For example, the polyol component may include a polyoxyethylene-polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt %, that has a nominal hydroxyl functionality from 2 to 6 (e.g., 2 to 4), and has a number average molecular weight from 500 g/mol to 5000 g/mol (e.g., 500 g/mol to 4000 g/mol, from 600 g/mol to 3000 g/mol, 600 g/mol to 2000 g/mol, 700 g/mol to 1500 g/mol, and/or 800 g/mol to 1200 g/mol). The polyoxyethylene-polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt % may account for 5 wt % to 90 wt % (e.g., 10 wt % to 90 wt %, 35 wt % to 90 wt %, 40 wt % to 85 wt %, 50 wt % to 85 wt %, 50 wt % to 80 wt %, and/or 55 wt % to 70 wt %) of the isocyanate-reactive component. The polyoxyethylene-polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt % may be the majority component in the isocyanate-reactive component.

The polyol component may include a polyoxypropylene-polyoxyethylene polyether polyol that has an ethylene oxide content of less than 20 wt % that has a nominal hydroxyl functionality from 2 to 6 (e.g., 2 to 4) and has a number average molecular weight greater than 1000 g/mol (or greater than 1500 g/mol) and less than 6000 g/mol. For example, the molecular weight may be from 1500 g/mol to 5000 g/mol, 1600 g/mol to 5000 g/mol, 2000 g/mol to 4000 g/mol, and/or 2500 g/mol to 3500 g/mol. The polyoxypropylene-polyoxyethylene polyether polyol that has an ethylene oxide content of less than 20 wt % may account for 5 wt % to 90 wt % (e.g., 5 wt % to 70 wt %, 5 wt % to 50 wt %, 10 wt % to 40 wt %, and/or 10 wt % to 30 wt %) of the isocyanate reactive component. The polyoxypropylene-polyoxyethylene polyether polyol that has an ethylene oxide content of less than 20 wt % may be in a blend with the polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt %, whereas the latter of which is included in a greater amount.

The polyol component may include a polyoxypropylene polyether polyol that has a nominal hydroxyl functionality from 2 to 6 (e.g., 2 to 4) and has a number average molecular weight from 500 g/mol to 5000 g/mol (e.g., 500 g/mol to 4000 g/mol, from 600 g/mol to 3000 g/mol, 600 g/mol to 2000 g/mol, 700 g/mol to 1500 g/mol, and/or 800 g/mol to 1200 g/mol). The polyoxypropylene polyether polyol may account for 5 wt % to 90 wt % (e.g., 5 wt % to 70 wt %, 5 wt % to 50 wt %, 10 wt % to 40 wt %, and/or 10 wt % to 30 wt %) of the isocyanate reactive component. The polyoxypropylene polyether polyol may be in a blend with the polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt %, whereas the latter of which is included in a greater amount.

In an exemplary embodiment, the polyol component may include a blend of the polyoxyethylene-polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt %, the polyoxyethylene-polyoxypropylene polyether polyol that has an ethylene oxide content of less than 20 wt %, and the polyoxypropylene polyether polyol.

The polyol component may be mixed with the preformed aqueous polymer dispersion (and optionally at least part of the additive component) before contacting the isocyanate component.

Additive Component

The additive component is separate from the components that form the preformed aqueous dispersion and the polyol component. The additive component is part of the isocyanate-reactive component, but other additives may be incorporated into the isocyanate component. The additive component may include a catalyst, a curing agent, a crosslinker, a surfactant, a blowing agent (aqueous and non-aqueous, separate from the aqueous polymer dispersion), a polyamine, a plasticizer, a fragrance, a pigment, an antioxidant, a UV stabilizer, water (separate from the aqueous polymer dispersion), and/or a filler. Other exemplary additives include a chain extender, flame retardant, smoke suppressant, drying agent, talc, powder, mold release agent, rubber polymer (“gel”) particles, and other additives that are known in the art for use in viscoelastic foams and viscoelastic foam products.

The additive component may include tin catalyst, zinc catalyst, bismuth catalyst, and/or amine catalyst. The total amount of catalyst in the isocyanate-reactive component may be from 0.1 wt % to 3.0 wt %.

A surfactant may be included in the additive component, e.g., to help stabilize the foam as it expands and cures. Examples of surfactants include nonionic surfactants and wetting agents such as those prepared by the sequential addition of propylene oxide and then ethylene oxide to propylene glycol, solid or liquid organosilicones, and polyethylene glycol ethers of long chain alcohols. Ionic surfactants such as tertiary amine or alkanolamine salts of long chain alkyl acid sulfate esters, alkyl sulfonic esters, and alkyl arylsulfonic acids may be used. For example, the formulation may include a surfactant such as an organosilicone surfactant. The total amount of an organosilicone surfactant in the isocyanate-reactive component may be from 0.1 wt % to 5.0 wt %, 0.1 wt % to 3.0 wt %, 0.1 wt % to 2.0 wt %, and/or 0.1 wt % to 1.0 wt %.

The additive component may include water, which is separate from the preformed aqueous polymer dispersion. The water may account for less than 2.0 wt % of the total weight of isocyanate-reactive component. The total water, including water from the preformed aqueous polymer dispersion and water from the additive component, may account for less than 5 wt % of the total weight of isocyanate-reactive component.

The additive component may exclude any conventional polyurethane foam chemical cell openers based on the use of the aqueous polymer dispersion. The additive component may exclude polybutene, polybutadiene, and waxy aliphatic hydrocarbons such as oils (e.g., mineral oil, paraffin oil, and/or naphthenic oil) that are commonly employed cell openers in low resiliency foams. The additive component may exclude cell openers that are polyols derived primarily from alkoxylation of α,β-alkylene oxides having at least 4 carbon atoms, e.g., as discussed U.S. Pat. No. 4,596,665. The additive component may exclude cell openers that are polyethers of up to about 3500 molecular weight that contain a high proportion (usually 50 percent or higher) of units derived from ethylene oxide or butylene oxide, e.g., as discussed in the background section of U.S. Pat. No. 4,863,976. The additive component may exclude cell openers that are polyether polyols having a molecular weight of at least 5000 and having at least 50 wt % of oxyethylene units, e.g., as discussed in the claims of U.S. Pat. No. 4,863,976.

Isocyanate Component

The isocyanate component includes at least one isocyanate. The isocyanate component is present at an isocyanate index from 50 to 110 (e.g., from 60 to 100, from 65 to 100, from 70 to 100, from 74 to 100, from 70 to 90, from 70 to 85, and/or from 74 to 85). The isocyanate index is defined as the molar stoichiometric excess of isocyanate moieties in a reaction mixture with respect to the number of moles of isocyanate-reactive units (active hydrogens available for reaction with the isocyanate moiety), multiplied by 100. An isocyanate index of 100 means that there is no stoichiometric excess, such that there is 1.0 mole of isocyanate groups per 1.0 mole of isocyanate-reactive groups, multiplied by 100.

The isocyanate component may include one or more isocyanate such as polyisocyanate and/or isocyanate-terminated prepolymer. The isocyanate may be isocyanate-containing reactants that are aliphatic, cycloaliphatic, alicyclic, arylaliphatic, and/or aromatic polyisocyanates or derivatives thereof. Exemplary derivatives include allophanate, biuret, and NCO (isocyanate moiety) terminated prepolymer. For example, the isocyanate component may include at least one aromatic isocyanate, e.g., at least one aromatic polyisocyanate or at least one isocyanate-terminated prepolymer derived from an aromatic polyisocyanate. The isocyanate component may include at least one isomer of toluene diisocyanate (TDI), crude TDI, at least one isomer of diphenyl methylene diisocyanate (MDI), crude MDI, and/or higher functional methylene polyphenyl polyisocyanate. Examples include TDI in the form of its 2,4 and 2,6-isomers and mixtures thereof and MDI in the form of its 2,4′-, 2,2′- and 4,4′-isomers and mixtures thereof. The mixtures of MDI and oligomers thereof may be crude or polymeric MDI and/or a known variant of MDI comprising urethane, allophanate, urea, biuret, carbodiimide, uretonimine and/or isocyanurate groups. Exemplary isocyanates include VORANATE™ M 220 (a polymeric methylene diphenyl diisocyanate available from The Dow Chemical Company). Other exemplary polyisocyanate include tolylene diisocyanate (TDI), isophorone diisocyanate (IPDI) and xylene diisocyanates (XDI), and modifications thereof.

Viscoelastic Foam

The viscoelastic polyurethane foam may be useful in a variety of packaging applications, comfort applications (such as mattresses—including mattress toppers, pillows, furniture, seat cushions, etc.) shock absorber applications (such as bumper pads, sport and medical equipment, helmet liners, etc.), and noise and/or vibration dampening applications (such as earplugs, automobile panels, etc.).

The viscoelastic polyurethane foam may be prepared in a slabstock process (e.g., as free rise foam), a molding process (such as in a box foaming process), or any other process known in the art. In a slabstock process, the components may be mixed and poured into a trough or other region where the formulation reacts, expands freely in at least one direction, and cures. Slabstock processes are generally operated continuously at commercial scales. In a molding process, the components may be mixed and poured into a mold/box (heated or non-heated) where the formulation reacts, expands without the mold in at least one direction, and cures.

The viscoelastic polyurethane foam may be prepared at initial ambient conditions (i.e., room temperature ranging from 20° C. to 25° C. and standard atmospheric pressure of approximately 1 atm). For example, the viscoelastic polyurethane foam may include an acid polymer and/or an acid-modified polyolefin polymer (e.g., a polymer that has a melting point above 100° C.) without requiring heating or application of pressure to the isocyanate-reactive component. Foaming at pressure below atmospheric condition can also be done, to reduce foam density and soften the foam. Foaming at pressure above atmospheric condition can be done, to increase foam density and therefore the foam load bearing as measured by indentation force deflection (IFD). In a molding processing, the viscoelastic polyurethane foam may be prepared at initial mold temperature above ambient condition, e.g., 50° C. and above. Overpacking of mold, i.e. filling the mold with extra foaming material, can be done to increase foam density.

The calculated total water content for the reaction system used to form the viscoelastic foam may be less than 5 wt %, less than 3 wt %, less than 2.0 wt %, and/or less than 1.6 wt %, based on the total weight of the reaction system for forming the viscoelastic polyurethane foam. The calculated total water content is calculated as the total amount of DI (deionized water) added to the formulation plus the amount of water added to the formulation as part of the preformed aqueous polymer dispersion. For example, the calculated total water content may be from 0.5 wt % to 1.6 wt %, 0.5 wt % to 1.5 wt %, and/or 1.0 wt % to 1.5 wt %.

The resultant viscoelastic polyurethane foam may exhibit improved wicking effect and/or improved moisture/heat management. With respect to moisture and heat management of a resultant foam, e.g., with respect to a viscoelastic polyurethane foam mattress or pillow, a good wicking effect may enable sweat to move quickly away from a user's skin. The key aspects of human body to maintain the comfort temperature are through moisture vapor by sweating. Sweating is the body's mechanism of keeping us cool. Good wicking effect may enable the user to remain dry and cool so as providing increased comfort. The good wicking effect may also provide the sweat/water with more surface area to evaporate from. Said in another way, as the sweat/water is dispersed over a greater area it may evaporate more rapidly than when the water is pooled together over a small surface area. Further, good moisture permeability may enable moisture to leave a user's skin and enable natural moisture vapor to bring heat away from the user's skin.

For example, the viscoelastic polyurethane foam may exhibit a visually observable wicking height (e.g., on a sample of the viscoelastic polyurethane foam having the dimensions of 1.0 inch×0.5 inch×2.0 inch, when an edge of the sample is submersed in 5.0 mm of dyed water) that is greater than a visually observable wicking height of a sample of a different viscoelastic polyurethane foam (which sample has the same dimensions) that is prepared using the same isocyanate-component, the same calculated total water content, and the same isocyanate-reactive component, except that the preformed aqueous polymer dispersion is excluded. For example, the wicking height may be greater by a factor of at least 3 (e.g., may be 3 to 10 times greater and/or 3.5 to 5.5 times greater).

The viscoelastic polyurethane foam may exhibit a visually observed wicking time (using a sample of the viscoelastic polyurethane foam), when three drops of dyed water are placed on a surface of the sample, that is less than a visually observed wicking time using a sample of a different viscoelastic polyurethane foam that is prepared using the same isocyanate-component, the same calculated total water content, and the same isocyanate-reactive component, except that the preformed aqueous polymer dispersion is excluded. As would be understanding, the compared samples may have a same thickness/depth, but the length and width of the samples are not dependent on the results. The wicking time is visually observed as the time at which it takes for three drops of dyed water to disappear (i.e., be absorbed by the foam) away from the surface of the samples. The wicking time may be decreased by at least 30 seconds so as to be significantly quicker when the preformed aqueous polymer dispersion is used. For example, the wicking time may be less than 5 seconds for the polyurethane foam prepared using the preformed aqueous polymer dispersion (e.g., greater than half a second).

The viscoelastic polyurethane foam may exhibit improved water vapor permeability, e.g., as measured according to ASTM E96/E96M (and optionally in view of ASTM E2321-03). For example, the water vapor permeability may be improved by at least 5% (e.g., from 5% to 20%) for the polyurethane foam prepared using the preformed aqueous polymer dispersion.

As would be understood by a person of ordinary skill in the art, the above comparison of two different foams refers to foams prepared using the same process conditions, same equipment, and the same formulations, except for the exclusion of the preformed aqueous polymer dispersion and the increased water content so as to account for excluding the preformed aqueous polymer dispersion in the comparative example.

All parts and percentages are by weight unless otherwise indicated. All molecular weight data is based on number average molecular weight, unless indicated otherwise.

Examples

The data and descriptive information provided herein are based on approximations. Further, the materials principally used are as the following:

AD 1 An aqueous acid polymer dispersion including approximately 21.7 wt % of a potassium hydroxide neutralized ethylene- acrylic acid copolymer salt and 78.3 wt % of water, made using a twin screw extruder and a dilution scheme as described in U.S. Pat. No. 8,318,257, is prepared as follows: A first feed includes 100 wt % of PRIMACOR ™ 5986 (an ethylene acrylic acid resin having approximately 20.5 wt % of acrylic acid) at a flow rate of 234 lb/h, a second feed includes 100 wt % of potassium hydroxide at a flow rate of 125 lb/h, and a third feed includes 100 wt % of water at a flow rate of 50 lb/h. A first dilution pump feeds water at 220 lb/h and a second dilution pump at 538 lb/h to achieve the desired solids content. The barrel/zone temperature control conditions are the following: Table 1 Zone Number Temperature ° C. Zone 1 27 Zone 2 151 Zone 3 147 Zone 4 148 Zone 5 161 Zone 6 149 Zone 7 107 Zone 8 109 Zone 9 80 Zone 10 131 Zone 11 72 Zone 12 72 AD 2 An aqueous acid polymer dispersion of approximately 32.3 wt % of an ammonium hydroxide neutralized ethylene acrylic acid copolymer salt and 67.7 wt % of water, prepared similar to as AD 1 except, the second feed is different and the dilution scheme is varied to achieve the desired higher solids content, as would be understood by one of ordinary skill in the art. AD 3 An aqueous dispersion of an aqueous acid- modified ethylene based copolymer, at a solids content from 40.5 wt % to 43.5 wt %, based on the total weight of the aqueous dispersion (available as HYPOD ™ 8503 from The Dow Chemical Company and enabled with BLUEWAVE ™ Technology). AD 4 An aqueous dispersion of an aqueous acid- modified polyolefin polymer, at a solids content from 54 wt % to 58 wt %, based on the total weight of the aqueous dispersion (available as HYPOD ™ XU-36534 from The Dow Chemical Company and enabled with BLUEWAVE ™ Technology). Polyol 1 A polyoxypropylene polyether polyol, having a nominal hydroxyl functionality of 3 and a number average molecular weight of approximately 1000 g/mol (available as VORANOL ™ 3150 from The Dow Chemical Company). Polyol 2 A glycerine initiated polyoxyethylene- polyoxypropylene polyether polyol, having an ethylene oxide content of approximately 60 wt %, a nominal hydroxyl functionality of 3, primary hydroxyl content of approximately 35%, and a number average molecular weight of approximately 1000 g/mol. Polyol 3 An polyoxypropylene-polyoxyethylene polyether polyol initiated with glycerine, having an ethylene oxide content of less than 20 wt %, a nominal hydroxyl functionality of 3, and a number average molecular weight of approximately 3100 g/mol (available as VORANOL ™ 3136 from The Dow Chemical Company). Isocyanate A polymeric methylene diphenyl diisocyanate - PMDI (available as PAPI ™ 94 from The Dow Chemical Company). Surfactant An organosilicone surfactant (available as Niax ™ L-618 from Momentive Performance Materials). Amine 1 A tertiary amine catalyst (available Dabco ® BL-11 from Air Products). Amine 2 A tertiary amine catalyst (available as Dabco ® 33-LV from Air Products). Tin A tin catalyst (available as KOSMOS ® 29 from Evonik Industries). DI Deionized Water.

Working Examples 1 to 3 and Comparative Examples A and B are prepared according to the approximate formulations in Table 2, below. In the Examples below, the total formulation mass is set to be 1900 grams. Working Examples 1 to 3 are prepared using one of AD 1 and AD 2, which are preformed aqueous acid dispersions. Comparative Example A is prepared using only water, i.e., not using a dispersion. Comparative Example B is an attempt at preparing a viscoelastic foam using ethylene-acrylic acid copolymer and water that are added separately, i.e., not using a preformed dispersion. However, due to the inability of ethylene-acrylic acid copolymer to dissolve in water at ambient conditions (it is believed, without intending to be bound by this theory, that a temperature of at least approximately 120° C. would be needed to melt the ethylene-acrylic acid copolymer crystals in water) such a mixture would be non-preferred and/or unsuitable for use in a foaming reaction for forming a viscoelastic foam. In other words, it is believed, the high temperature required to obtain solubility would be non-preferred and/or unsuitable for the purpose herein and/or non-dissolved ethylene-acrylic acid copolymer crystals would be non-preferred and/or unsuitable for the purpose herein. The density of the samples range from approximately 2.7 to 3.0 lb/ft³ (according to ASTM D 3574).

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. A Ex. B Isocyanate-Reactive Component (amount based on parts by weight) AD 1 1.40 1.40 — — — AD 2 — — 1.62 — — PRIMACOR ™ — — — — 1.40 5986 DI 1.10 1.10 1.10 2.20 2.20 Polyol 1 20.00 20.00 20.00 20.00 20.00 Polyol 2 60.00 60.00 60.00 60.00 60.00 Polyol 3 20.00 20.00 20.00 20.00 20.00 Surfactant 0.80 0.80 0.80 0.80 0.80 Amine 1 0.15 0.15 0.15 0.15 0.15 Amine 2 0.05 0.05 0.05 0.05 0.05 Tin 0.05 0.05 0.05 0.05 0.05 Isocyanate Component (amount based on parts by weight) Isocyanate 53.35 52.01 53.35 53.35 53.35 Composition Properties Approximate 156 156 157 156 156 Total Parts Index 80 78 80 80 80 AD wt % in 1.35 1.35 1.56 — — Isocyanate- Reactive Component Calculated 2.20 2.20 2.20 2.20 2.20 Total Water Content (parts by weight) Foam Properties Air Flow (scfm) 8.5 8.4 7.9 3.4 * Average 5.2 — 4 4 * Resiliency (%) Recovery Time 3 5 3 3 * (seconds) IFD @ 25% 8.2 9.9 7.8 14.0 * Deflection (lb) IFD @ 65% 17.6 21.1 16.1 28.3 * Deflection (lb) IFD @ 25% 7.1 8.3 6.9 12.5 * Return (lb) * Unable to form a viscoelastic foam because the PRIMACOR ™ 5986 did not dissolve in water at ambient conditions.

Working Examples 4 to 11 and Comparative Example C are prepared according to the approximate formulations in Table 3, below. In the Examples below, the total formulation mass is set to be 1900 grams. Working Examples 4 to 11 are prepared using one of AD 3 and AD 4, which are preformed aqueous acid-modified polyolefin dispersion. Comparative Example C is prepared using only water, i.e., not using a dispersion. The density of the samples range from approximately 2.5 to 3.0 lb/ft³ (according to ASTM D 3574).

TABLE 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. C Isocyanate-Reactive Component (amount based on parts by weight) AD 3 2.20 0.77 0.77 1.91 — — — — 1.91 — AD 4 — — — — 0.51 1.01 1.52 2.53 — — DI 1.10 1.98 1.76 1.10 1.98 1.76 1.54 1.10 1.10 2.20 Polyol 1 15.00 15.00 15.00 15.00 15.00 15.00 15.00 15.00 20.00 15.00 Polyol 2 60.00 60.00 60.00 60.00 60.00 60.00 60.00 60.00 60.00 60.00 Polyol 3 25.00 25.00 25.00 25.00 25.00 25.00 25.00 25.00 20.00 25.00 Surfactant 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 Amine 1 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Amine 2 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Tin 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Isocyanate Component (amount based on parts by weight) Isocyanate 51.00 50.99 50.99 50.99 50.99 50.99 50.99 50.99 51.48 50.99 Composition Properties Approximate 155 154 155 155 155 155 155 155 156 154 Total Parts Index 75 78 78 78 78 78 78 78 77 78 AD wt % in 2.11 0.74 0.74 1.84 0.50 0.97 1.46 2.42 1.84 — Isocyanate- Reactive Component Calculated 2.37 2.20 2.20 2.20 2.20 2.20 2.20 2.20 2.20 2.20 Total Water Content (parts by weight total) Foam Properties Air Flow 8.9 5.6 6.2 9.7 5.4 6.1 7.3 9.6 7.3 4.1 (scfm) Average 6 4 4 5 3 4 4 4 5 3 Resiliency (%) Recovery Time 7 3 3 5 3 4 4 4 2 3 (seconds) IFD @ 25% 5.2 8.4 8.3 5.9 8.8 8.8 7.9 5.8 11.4 10.7 Deflection (lb) IFD @ 65% 11.6 18.6 18.4 13.2 19.1 19.2 17.3 13.2 25.9 22.6 Deflection (lb) IFD @ 25% 4.2 7.3 7.2 4.9 7.8 7.5 6.7 5.0 10.2 9.4 Return (lb)

For each of Working Examples 1 to 11 and Comparative Examples A to C, foam samples are prepared by box foaming at ambient conditions, under a fume hood using a 38 cm×38 cm×24 cm (15″×15″×9.5″) wooden box lined with clear plastic film. A 16-pin (4 pins each in four radial directions that are separated by 90°) mixer at high rotation speed is used at high rotation speed setting, together with a 1 gallon cup (16.5 cm diameter, 18 cm tall). The components in the Isocyanate-Reactive Component, with the exception of the Tin catalyst, are mixed first for 15 seconds at 2400 rpm. Then, the Tin catalyst is added and immediately mixed for another 15 seconds at 2400 rpm. Next, the Isocyanate Component is added and immediately mixed for another 3 seconds at 3000 rpm. Then, the mixed Isocyanate-Reactive Component and Isocyanate Component is poured into the box lined with plastic film. The foam is observed as having reached maximum height when bubbles appear at the top surface of the foam. Once foaming is complete, the foam is further allowed to cure overnight under the fume hood. Foam sample walls are discarded, and the remaining samples are characterized.

For Working Example 12, the foam is made using a Cannon Varimax foaming machine. The Polyol 1 and Polyol 3 are used as a blend with a ratio of 1:1. The total polyol flow rate targets 110 lb/min. A foam bun is made with the size of approximately 96 inch×52 inch×20 inch. The resultant foam sample is cut a day after the foam is fabricated. Then, the samples are conditioned for 24 hours before the physical property tests are performed.

Calculated Total Water Content (parts by weight) is calculated as the total amount of DI (deionized water) added to the formulation plus the amount of water added to the formulation as part of the aqueous dispersion.

Air flow is a measure of the air that is able to pass through the foam under a given applied air pressure. Air flow is measured as the volume of air which passes through a 1.0 inch (2.54 cm) thick×2 inch×2 inch (5.08 cm) square section of foam at 125 Pa (0.018 psi) of pressure. Units are expressed in standard cubic feet per minute (scfm). A representative commercial unit for measuring air flow is manufactured by TexTest AG of Zurich, Switzerland and identified as TexTest Fx3300. Herein, air flow is measured according to ASTM D 3574.

Average resiliency is measured according to ASTM D 3574, in particular using the ball rebound test. Recovery time is measured is measured by releasing/returning the compression load head from a 75% position (i.e., the foam sample is compressed to 100% minus 75% of the sample's original thickness) to the position where foam compression is to a 10% position (based on the original thickness of the foam sample). The Recovery Time is defined as the time from the releasing/returning the compression load head to the moment that the foam pushes back against the load head with a force of at least 1 newton.

IFD is referred to as indentation force deflection and it is measured according to ASTM D 3574. IFD is defined as the amount of force in pounds required to indent a fifty square inch circular plate sample a certain percentage of the sample's original thickness. Herein, IFD is specified as the number of pounds at 25% deflection and at 65% deflection for the foam sample. Lower IFD values are sought for viscoelastic foams. For example, an IFD at 25% from 6 to 12 may be used for bed pillows, thick back pillows, etc. An IFD at 25% from 12 to 18 may be used for medium thickness back pillows, upholstery padding, etc. An IFD at 25% from 18 to 24 may be used for thin back pillows, tufting matrix, very thick seat cushions, etc. An IFD at 25% greater than 24 may be used for average to firmer seat cushions, firm mattresses, shock absorbing foams, packaging foams, carpet pads, and other uses requiring ultra-firm foams.

IFD at 25% Return is the ability of the foam to recover. In particular, the IFD at 25% Return is measured as the percentage of the IFD at 25% that is recovered after cycling through the IFD at 65% measurement and returning to 25% compression.

As used herein, the term “tear strength” is used herein to refer to the maximum average force required to tear a foam sample which is pre-notched with a slit cut lengthwise into the foam sample. The test results are determined according to the procedures of ASTM D3574-F in pound-force per linear inch (lbf/in) or in Newtons per meter (N/m).

Wicking Effect and Moisture/Heat Management

Working Example 12 is further evaluated for wicking and moisture/heat management, as combined with the high airflow. To test the wicking wetting effect, Comparative Example D is prepared using the same method and formulation as Working Example 12, except Additive 3 is not added to the formulation.

To realize a good wicking effect, the materials should have a good wetting effect. FIG. 2 illustrates the wetting effect on the foam sample of Working Example 12 and FIG. 3 illustrates the wetting effect on the foam sample of Comparative Example D. To perform the wetting effect, three drops of dyed water are put on the surface of the respective foam samples having a thickness of 1.0 inch and the time at which it takes for the drops of water to disappear from the surface is visually observed and recorded as the wicking time. The water is dyed with an orange dye available from Milliken Chemical. Working Example 12 is visually observed to have a faster wicking speed and the water drops are wicked away from the surface of the sample at a wicking time of approximately 1 second and Comparative Example D is visually observed to have a slower wicking speed with a wicking time of 38 seconds. Accordingly, it is seen that when the foam samples for are made using the same conditions and formulations, except that the preformed aqueous polymer dispersion is excluded in the comparative example, that the wicking speed is quicker and the wicking time is lower by approximately 37 seconds, when the preformed aqueous polymer dispersion is included.

Wicking height may also be testing using a vertical wicking test. In particular, foam samples having the dimensions of 1.0 inch×0.5 inch×2.0 inch are prepared for Working Example 12 and Comparative Example D. The tips of the foam samples are immersed in 5.0 mm of the dyed water, while the foam samples are maintain in a substantially vertical position relative to the horizontal dish holding the dyed water. Vertical wicking, i.e., upward movement, of the water is enabled for 1 minute (at ambient conditions). Then, the upward movement is measured using a ruler and recorded as the vertical wicking height. Working Example 12 is measured as having a vertical wicking height of 6.35 mm and Comparative Example D is measured as having a vertical wicking height of 1.59 mm. Accordingly, it is seen that when the foam samples are made using the same conditions and formulations, except that the preformed aqueous polymer dispersion is excluded in the comparative example, that the wicking height is increased by a factor of approximately 4 when the preformed aqueous polymer dispersion is included.

The water vapor permeability of Working Example 12 and Comparative Example D may be testing. In particular, a standard cup desiccant method is conducted following ASTM E96/E96M. Further, ASTM E2321-03 is followed for the Standard Practice, a petri dish method (the diameter of the petri dish is 5.5 inch). For testing each of Working Example 12 and Comparative Example D, three specimens are used, of which specimens are foam samples that have a thickness of approximately 1.30 inches and that have their edges sealed with wax (e.g., wax that is melted at approximately 140° F.). To test the water vapor permeability, the petri dish is filled up to within ¼ in of the top rim. During testing the humidity level is 72.7% and the temperature control is 50.8° F.

Working Example 12 is observed as having a water vapor permeability of approximately 71.6 (grains/hour/ft²)/ΔP×inches and Comparative Example D is observed as having a significantly lower water vapor permeability of approximately 67.4 (grains/hour/ft²)/ΔP×inches. Accordingly, it is seen that when the foam samples are made using the same conditions and formulations, except that the preformed aqueous polymer dispersion is excluded in the comparative example, that the water vapor permeability may be improved by approximately 5.9% when the preformed aqueous polymer dispersion is included. 

1. A reaction system for forming a viscoelastic polyurethane foam that has a resiliency of less than or equal to 20% as measured according to ASTM D 3574, the reaction system comprising: an isocyanate component that includes at least one isocyanate, an isocyanate index of the reaction system being from 50 to 110; and an isocyanate-reactive component that is a mixture formed by adding at least a polyol component, an additive component, and a preformed aqueous polymer dispersion, the mixture including: from 50.0 wt % to 99.8 wt % of a polyol component, based on the total weight of the mixture, the polyol component including at least one polyether polyol, from 0.1 wt % to 50.0 wt % of an additive component, based on the total weight of the mixture, that includes at least one catalyst, and from 0.1 wt % to 6.0 wt % of a preformed aqueous polymer dispersion, based on the total weight of the mixture, the preformed aqueous polymer dispersion having a solids content from 10 wt % to 80 wt %, based on the total weight of the preformed aqueous polymer dispersion, and being one of an aqueous acid polymer dispersion or an aqueous acid-modified polyolefin polymer dispersion in which the polyolefin is derived from at least one C₂ to C₂₀ alpha-olefin.
 2. The reaction system as claimed in claim 1, wherein the preformed aqueous polymer dispersion is a continuous liquid phase component at ambient conditions of room temperature and atmospheric pressure and is derived from a liquid phase and a solid phase, the liquid phase being water and the solid phase being an acid or an acid-modified polyolefin in which the polyolefin is derived from at least one C₂ to C₂₀ alpha-olefin.
 3. The reaction system as claimed in claim 1, wherein the preformed aqueous polymer dispersion is a continuous liquid phase component at ambient conditions of room temperature and atmospheric pressure and is derived from a liquid phase and a solid phase, the liquid phase being water and the solid phase including an ethylene-acrylic acid copolymer.
 4. The reaction system as claimed in claim 1, wherein the preformed aqueous polymer dispersion is separately provided from the polyol component and the additive component.
 5. The reaction system as claimed in claim 1, wherein the additive component includes at least one surfactant.
 6. The reaction system as claimed in claim 1, wherein the additive component includes water that accounts for less than 2.0 wt % of the total weight of mixture.
 7. The reaction system as claimed in claim 1, wherein the polyol component includes at least one polyoxyethylene-polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt %, has a nominal hydroxyl functionality from 2 to 4, and accounts for 35 wt % to 90 wt % of the isocyanate-reactive component.
 8. The reaction system as claimed in claim 1, wherein the polyol component includes a blend of at least three polyols, the blend including: (i) a polyoxyethylene-polyoxypropylene polyether polyol that has an ethylene oxide content of at least 50 wt %, has a nominal hydroxyl functionality from 2 to 4, has a molecular weight from 700 g/mol to 1500 g/mol, and accounts for 35 wt % to 90 wt % of the isocyanate-reactive component, (ii) a polyoxypropylene-polyoxyethylene polyether polyol that has an ethylene oxide content of less than 20 wt %, has a nominal hydroxyl functionality from 2 to 4, has a molecular weight greater than 1500 g/mol and less than 6000 g/mol, and accounts for 5 wt % to 50 wt % of the isocyanate-reactive component, and (iii) a polyoxypropylene polyether polyol that has a nominal hydroxyl functionality from 2 to 4, has a molecular weight from 700 g/mol to 1500 g/mol, and accounts for 5 wt % to 50 wt % of the isocyanate-reactive component.
 9. A viscoelastic polyurethane foam that has a resiliency of less than or equal to 20%, as measured according to ASTM D 3574, prepared using the reaction system as claimed in claim 1, the viscoelastic foam having an air flow of at least 5.0 ft³/min as measured according to ASTM D3574, and a recovery time of less than 20 seconds.
 10. The viscoelastic polyurethane foam as claimed in claim 9, wherein a visually observed wicking height of a sample of the viscoelastic polyurethane foam, having the dimensions of 1.0 inch×0.5 inch×2.0 inch, when an edge of the sample is submersed in 5.0 mm of dyed water, is greater than a visually observed wicking height of a similar sample of a viscoelastic polyurethane foam, which similar sample as the same dimensions, that is prepared using the same isocyanate-component, a same calculated total water content, and the same isocyanate-reactive component, except that the preformed aqueous polymer dispersion is excluded.
 11. The viscoelastic polyurethane foam as claimed in claim 9, wherein using a sample of the viscoelastic polyurethane foam, a visually observed wicking time, when three drops of dyed water are placed on a surface of the sample, is less than a visually observed wicking time using a similar sample of a viscoelastic polyurethane foam, which similar sample as the same dimensions, that is prepared using the same isocyanate-component, a same calculated total water content, and the same isocyanate-reactive component, except that the preformed aqueous polymer dispersion is excluded.
 12. A method for forming a viscoelastic polyurethane foam that has a resiliency of less than 20% as measured according to ASTM D 3574, the method comprising: preparing an isocyanate-reactive component by mixing at least a polyol component, an additive component, and a preformed aqueous dispersion, the resultant mixture including: from 50.0 wt % to 99.8 wt % of a polyol component, based on the total weight of the mixture, the polyol component including at least one polyether polyol, from 0.1 wt % to 50.0 wt % of an additive component, based on the total weight of the mixture, that includes at least one catalyst and at least one surfactant, and from 0.1 wt % to 6.0 wt % of a preformed aqueous polymer dispersion, based on the total weight of the mixture, the preformed aqueous polymer dispersion having a solids content from 10 wt % to 80 wt % based on the total weight of the preformed aqueous polymer dispersion and being one of an aqueous acid polymer dispersion or an aqueous acid-modified polyolefin polymer dispersion in which the polyolefin is derived from at least one C₂ to C₂₀ alpha-olefin; providing an isocyanate component that includes at least one isocyanate such that an isocyanate index of the reaction system is from 50 to 110; and allowing the isocyanate component to react with the isocyanate-reactive component to form the viscoelastic polyurethane foam. 